Labors of Heracles - Mares of Diomedes
Drat I couldn't find a good piece of ancient art for this one!
Heracles was next ordered by Eurystheus to bring the Mares of Diomedes the Thracian ruler of the Bistones to him. Now these horses were said to be man eaters or at least wild and dangerous.
This myth goes on to explain or rather claim that a man called Abderos was killed by the horses and that Heracles founded a city named after him.
There was certainly an Ionian colony there much later.
As for whether or not the mares were monsters horses wild or not can turn on humans and bite and kick.
I imagine these horses would indeed react violently if they were only used for breeding never ridden and suddenly lead away by strangers from their stables?
One version of the story mentions Heracles cutting a canal to form a lake to stop Diomedes pursuing him.
There is a lake nearby with a narrow entrance to the sea.
This is an explanation of myths used to explain origins.
The Greeks often used claims of settlements in the Mycenaean era to justify building colonies later though perhaps there could have been some kind of trading post before the Greek city was built?